The present invention relates to an arrangement for open-end spinning comprising a driven suction roller for taking up fiber material which has been opened to single fibers and for transporting the fiber material from a take-up zone to a suctioned yarn formation line, which is defined by a suction insert arranged in the inside of the suction roller and which extends on the surface of the suction roller transversely to the transport direction thereof, whereby a twist device is provided in extension of the yarn formation line in close proximity to the suction roller.
In the case of an arrangement of this type (U.S. Pat. No. 5,241,813), the functions of collecting the single fibers, binding the single fibers into the forming yarn and imparting a twist to the yarn are all separate from one another. As the yarn, as long as it is disposed at the yarn formation line on the surface of the suction roller, obtains only a relatively slight pre-twist at first, there is a risk that the continually new forming yarn tips will hang down from the continuously withdrawn yarn or at least that from time to time thin spots form in the yarn. This is in particular the case when, in order to avoid crimping of the single fibers at the yarn formation line, the yarn is withdrawn at a speed which is higher than the arrival speed of the single fibers at the yarn formation line. In this case of the prior art, the dwell time of the continually renewing yarn tip in the yarn formation line is extremely short, so that a sufficiently intensive and timely twist is not guaranteed. Even if the twist device is arranged relatively near to the suction roller, there still exists a certain unguided section of the collected fibers between the suction roller and the twist device.
It is an object of the present invention, in the case of an arrangement of the above mentioned type to improve twist impartation in the forming yarn, in particular at high yarn withdrawal speeds.
The object of the present invention is achieved by the invention in that the suction roller, on the side facing away from the twist device, is supported on the suction insert while freely overhanging same, and the suctioned yarn formation line reaches in direct proximity to the twist device.
By means of the constructive embodiment of the bearing of the suction roller, there are no bearing elements between the twist device and the suction roller, so that there is almost no unguided section of the fiber accumulation between the twist device and the suction roller. The twist device can thus be brought to the point at which the fiber accumulation ends at the yarn formation line. The last single fibers fed to the yarn formation line reach an almost finished yarn when the twist device adjoins the collecting area with no space in between.
Free overhanging suction rollers are known from German published patent application 33 16 658, but not in connection with a twist device arranged downstream. The purpose of the known free overhanging bearing is rather more that one end of the sleeve of the suction roller is left free, so that cleaning of the interior of the sleeve from this side is possible.
The twist device can be guided particularly near to the yarn formation line when it takes the form of a spinning jet, as is known in principle from pneumatic false twist spinning. The single fibers reach the yarn formation line directly upstream of the entry opening of the yarn in the spinning jet. This jet determines the final extent of the twist.
In an advantageous embodiment of the invention it is provided that the yarn formation line is bent towards the take-up zone on the side facing away from the twist device. The continuously renewing yarn tip obtains a certain thrust in transport direction therefrom, which lessens the longitudinal tension in the area of the yarn tip. The risk of yarn tips hanging from the withdrawn yarn and the risk of thin spots are thus reduced. By altering the angle of the bend, the transport thrust on the yarn and the longitudinal tension of the withdrawn yarn can be altered as required.
The yarn formation line can be guided to within the area of the take-up zone and can extend at least approximately in transport direction of the suction roller. Thus the transport thrust is at its strongest in the area of the outermost yarn tip at a practically negligibly low tension. The more the yarn is bent in the direction towards the yarn formation line, the weaker the transport thrust becomes, while the longitudinal tension in contrast becomes stronger. The longitudinal tension is at its highest after receiving the last single fibers, directly upstream of the twist device. It is hereby favorable when the yarn tip transfers to the actual yarn formation line over a rounded transition point.
In order to increase the pre-twist to the yarn, a supplementary roller driven in the same direction as the suction roller can be arranged thereto, which supplementary roller forms a wedge-shaped gap together with the suction roller, at least in the area of the yarn formation line arranged at the twist device. As the transport speed of the suction roller should be lower than the withdrawal speed of the yarn and is thus limited in its range, the supplementary roller, in particular when it is subject to slip, can be driven at an increased speed. The supplementary roller may also take the form of a nipping roller. The pre-twist is then more secure, with less slip, and the yarn obtains in its formation phase a degree of tensile strength.
For the purpose of the present invention it is advantageous when the suction effect of the suction insert is stronger in the area of the yarn formation line than in the remaining areas. The yarn formation line is thereby exactly defined, in particular when the fiber tip is bent in the direction towards the take-up zone.